title: Autoinhibition of endothelial nitric oxide synthase (eNOS) in gut smooth muscle by nitric oxide.
abstract: Nitric oxide in the gut is produced by nNOS in enteric neurons and by eNOS in smooth muscle cells. The eNOS in smooth muscle is activated by vasoactive intestinal peptide (VIP) released from enteric neurons. In the present study, we examined the effect of nitric oxide on VIP-induced eNOS activation in smooth muscle cells isolated from human intestine and rabbit stomach. NOS activity was measured as formation of the 1:1 co-product, l-citrulline from l-arginine. VIP caused an increase in l-citrulline production that was inhibited by NO in a concentration dependent manner (IC(50)~25 microM; maximal inhibition 72% at 100 microM NO). Basal l-citrulline production, however, was unaffected by NO. The effect was not mediated by cGMP/PKG since the PKG inhibitor KT5823 had no effect on eNOS autoinhibition. The autoinhibition was selective for NO since the co-product l-citrulline had no effect on VIP-induced NOS activation. Similar effects were obtained in rabbit gastric and human intestinal smooth muscle cells. The results suggest that NO produced in smooth muscle cells as a result of the activation of eNOS by VIP exerts an autoinhibitory restraint on eNOS thereby regulating the balance of the VIP/cAMP/PKA and NO/cGMP/PKG pathways that regulate the relaxation of gut smooth muscle.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Box 980551, Virginia Commonwealth University, Richmond, VA 23298, United States. jgrider@vcu.edu
authors.forename: John R
authors.initials: JR
authors.lastname: Grider
authors.forename: Karnam S
authors.initials: KS
authors.lastname: Murthy
mesh_terms: D000818:Animals; D002956:Citrulline / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006706:Homeostasis; D006801:Humans; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis* / Q000494:pharmacology; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011706:Pyloric Antrum / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D002956:Citrulline; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III